1. Field of Invention
The invention relates, generally, to lighting equipment for a motor vehicle and, more specifically, to a light source with a gas-discharge lamp employed with such lighting equipment.
2. Description of Related Art
A light source of the related art is known from, for example, “WO 2004/083900A1” or “WO 2004/084250A1.” In one of the gas-discharge lamps described there, inert gas or a gas mixture is contained in a burner, which can also be described as a “discharge vessel” or “inner bulb.” Voltage is applied between two electrodes extending into the interior of the burner, forming an electric arc between the electrodes, which results in light emission. The electric arc can be maintained while the light source is operating. In the process, a driver circuit of a control module or a control unit of the gas-discharge lamp generates from the 12- or 24-V-battery charge an intermediate voltage of several hundred volts up to more than 1,000 V—for example, approximately 1,200 V—that are applied between the two potentials of −700 and +500 V. From this intermediate voltage, an ignition module of the gas-discharge lamp generates an ignition voltage (high voltage) for the burner, which can amount to several kilovolts—for example, in the range of between 10 and 25 kV (specifically, 23 kV). To ignite the electric arc, the ignition voltage is applied to the electrodes. When the electric arc has been ignited, the voltage that is applied at the electrodes can be reduced to a supply voltage (AC voltage) of merely several volts—for example, 43 or 85 V at 400 Hz. The supply voltage is supplied by a driver circuit of the control module. The ignition voltage can be generated by stepping up the supply voltage.
The known light sources have a separate control module that is arranged spatially separated from the burner. The ignition module is integrated in the control module or arranged directly at the burner and/or a socket of the gas-discharge lamp. The supply voltage generated by the control module is guided to the burner or ignition module via a shielded conduit and applied to the electrodes. In the known gas-discharge lamps, the control module is decentralized for thermic reasons. For example, the driver circuit designed in the control module includes several electronic components that generate, for the most part, a considerable quantity of heat during the time of operating the light source. This heat can be easily discharged at a distance from the burner where the ambient temperatures are not so high. The electric arc that is ignited and maintained inside the burner generates extremely high temperatures that can amount to several-hundred degrees Celsius and can reach 1,000° C. and more. These high temperatures would adversely affect or even damage the driver circuit or its electronic components if the control module was arranged in close proximity of the burner.
However, the known light sources have the disadvantage that they require a relatively large space because the control module is arranged separately from the remaining part of the light source. Moreover, the shielded connecting cable required between the control module and remaining part of the light source (the burner or ignition module) results in additional costs and an increase in expenses during assembly. Because of the AC signals transmitted via the connecting cable and the resulting electromagnetic radiation, it is required that the connecting cable be well-shielded against electromagnetic radiation. This is achieved by, for example, surrounding the connecting cable with a metal mesh or metal/plastic mesh. However, this mesh has to fulfill a number of requirements that, in turn, results in relatively high costs for the shielded connecting cable. For example, if the light source is part of a movable light module, the mesh has to be flexible enough such that the shielded connecting cable does not adversely or significantly affect a movement of the burner in relation to the control module. Otherwise, a reliable movement, especially a steady movement, of the light module cannot be guaranteed, or it requires especially strong forces and especially large and heavy drive units.
Thus, there is a need in the related art for a light source including a gas-discharge lamp that is compact, easy to use, and cost-effective.